Here is a simple instruction for you:
00. power on your PS4, but do not run GT sport
01. restore your Cross Hair
02. add only "GT sport"'s config in Cross Hair, and save
03. turn of PS4 controller
by holding PS Button on controller for about 20 seconds until the controller's light bar is off.
04. firstly, connect PS4 controller and G27 to Cross Hair,
and then connect Cross Hair to PS4
(when Cross Hair is breathing,the color is defined in the activated config, PS4 controller will work in wired mode)
05. run GT sport on PS4, using buttons on G27 shifter or PS4 controller
06. try the wheel and paddles in game
(PS4 controller should not be in wireless mode during this)